This invention relates to the granulation of rehydratable alumina in small particle sizes.
Alumina, as a chemical compound by itself or in combination with one or more other refractory inorganic oxides, is widely employed in industrial process applications as a catalyst, as a catalyst base, as a support or chemical carrier material, or as an adsorbent. The granulation of alumina powders to form granular aluminas is one of the crucial tasks in preparing aIumina for one of the various types of industrial process applications. Granulation improves the bulk properties of the alumina in particulate form. The substitution of granular aluminas for fine powders can create beneficial effects including improved pore structure, improved flow properties, reduced dusting loss, and improved product appearance. The beneficiation of granulation can be accomplished by techniques classified into several categories according to the principal method used for the beneficiation including, e.g., agitation in a tumbling drum, pressure, thermal, spray in a fluidized bed, and agglomeration from liquids by an oil drop method. As each method is different in technique of beneficiation, the resulting granular product also is characteristically different in properties.
In the granulation of powdered materials, binding is partially achieved by liquid-solid capillary energy reduction. In both alumina granulation and alumina hydrate granulation, water sometimes has been used as the liquid binder.
Alumina has numerous crystalline forms. Strictly speaking, so-called "activated" alumina includes eta, chi, gamma, and rho-alumina, of which the specific surfaces are in the range of about 100-400 m.sup.2 /g. These activated alumina forms are important substrates for the various industrial process applications. Activated alumina generally is produced by dehydration reactions from alumina hydrate such as gibbsite, bayerite, boehmite, and an amorphous gel. The alumina hydrates can be converted into various forms of alumina depending on dehydration conditions.
It is an object of the present invention to prepare small granules of activated alumina.
It is another object of the present invention to prepare activated alumina having a high surface area and small granular particle size.
It is yet another object of the present invention to prepare an activated eta-alumina or gamma-alumina having a high surface area in a small granular particle size.